As energy prices are increasing due to depletion of fossil fuels and interest in environmental pollution is on the rise, demand for environmentally friendly alternative energy sources is bound to play an increasing role in future life. Thus, research into various power generation techniques such as nuclear energy, solar energy, wind energy, tidal power, and the like, continues, and power storage devices for more efficient use of the generated energy are also drawing much attention.
In particular, demand for lithium secondary batteries as energy sources is rapidly increasing as mobile device technology continues to develop and demand therefor continues to increase. Recently, use of lithium secondary batteries as a power source of electric vehicles (EVs) and hybrid electric vehicles (HEVs) has been realized and use thereof continues to expand to applications such as auxiliary power supplies through smart-grid technology.
Anodes of conventional lithium secondary batteries mainly use, as an anode active material, carbon-based compounds that maintain structural and electrical properties and enable reversible intercalation and deintercalation of lithium ions. However, recently, research into anode materials prepared by alloying Li with silicon (Si) or tin (Sn) and lithium titanium oxides instead of conventional carbon-based anode materials has been underway.
Lithium titanium oxides are materials that hardly undergo structural changes during charging and discharging and thus exhibit zero strain. In addition, lithium titanium oxides are known to have excellent lifespan characteristics, have a relatively high voltage range, and not to form dendrites, thus exhibiting excellent safety and stability.
However, such lithium titanium oxides require a larger amount of binder than conventional carbon-based anode active materials due to wide surface area thereof. When the amount of the binder in an electrode increases, the thickness of the electrode increases to realize the same capacity and cell resistance increases. In this regard, the cell resistance increases as a binder having a higher molecular weight is used.
Adhesion of an electrode affects electrode processability and electrode performance stability. Insufficient adhesion causes electrode separation during drying, pressing, and the like of an electrode and thus increases an electrode defect rate. In addition, separation of an electrode with low adhesion even by external impact to a battery may adversely affect lifespan characteristics and the like of the battery and such electrode separation increases contact resistance between an electrode material and a current collector, which is a cause of reduction in electrode output performance.
However, when the amount of binder increases in order to address adhesion problems, the amount of active material decreases and the binder acts as a resistance in an electrode and, accordingly, battery performance is deteriorated.
Therefore, there is a very urgent need to develop technology for enhancing battery capacity by securing adhesion between an active material and a current collector and enhancing overall battery performance.